Mitochondria are membrane-limited subcellular organelles that contain their own DNA and metabolic systems; they function as the powerhouses of mammalian cells. Organs that are most metabolically active have the highest need for energy, and also have the highest number of mitochondria per cell.
Genetic and acquired mitochondrial defects that results in dysfunction cause disease and frequently early death due to liver damage. Genetic defects are rare; but are usually fatal early in life. Acquired mitochondrial damage due to drug toxicity, however, is relatively common, and can lead to severe morbidity and death in adults. There are currently no cures for mitochondrial defects or damage.